Device for preventing seizure of magnetron tuning mechanism



Nov. 12, 1957 A. M. I-YIANFMANN 2,812,993

DEvIcE FOR PREVENTING SEIZURE 0F MAGNETRON TUNING MECHANISM Filed Aug. 26, 1954- ZIMM cqz/M PUMP V I DEVICE FOR PREVENTING SEIZURE OF MAGNETRON TUNING MECHANISM Alexander M. Hanfmann, Allentown, Pa., assignor to Western Electric Company, Incorporated, New York,

N. Y.,' a corporation of New York Application August 26, 1954, Serial No. 452,291

2 Claims. (Cl. 31630) This invention relates to magnetrons and particularly to problems arising during their manufacture due to the necessity of subjecting them for long periods to relatively high temperatures.

As is well understood in the art, it is'necessary to exhaust the air from the resonant cavities of a magnetron before the tube can be used. In order to produce the high degree of vacuum required, it is necessary to place the tube in a heated oven during the pumping operation and the resulting high temperature of the working parts tends to cause a rapid formation of scale due to oxidation of the metal. Any appreciable scale formed on the working parts, such as the movable tuning head and its bearing surfaces, causes the tuning head to seize and makes the tube inoperable.

' To inhibit the formation of this scale it has been the practice to provide an inert atmosphere within the tuning head by supplying a suitable gas such as nitrogen thereto while the magnetron is being pumped. It has been found, however, that this is not always effective and in such cases it has been necessary to break the vacuum, remove the tube from theexhaust station and, if possible, forcibly free the tuning mechanism. Even when units could be salvaged in this manner it was accomplished only at considerable expense particularly since the exhausting opera- Ition had to be repeated without any assurance that the second operation would be successful.

The object of this invention is to eliminate this salvaging operation and the loss of product due to seizure of the tuning head.

According to the general features of the invention, the inert gas is supplied to a magnetron during the exhausting operation in such a manner as not to obstruct access to the tuning mechanism and means are provided externally of the oven by which the tuning mechanism may be op-- erated at intervals thereby repeatedly breaking the scale as it forms and preventing it from accumulating in sufficient quantity to cause seizure of the mechanism.

These and other features of the invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

Fig. 1 is an elevational view of an embodiment of the invention adapted for use with a magnetron in a high temperature oven and exhausting chamber, and

Fig. 2 is an enlarged view of a portion of Fig. 1 showing the details of the actuating mechanism for the magnetron tuning head.

Referring now to the drawing, a magnetron 4 is mounted by means of a support member 7 in a baking oven compartment 5 Where the resonant cavity of the magnetron besides being heated to a high temperature, is exhausted by a vacuum pump (not shown) externally connected thereto through a tube 6 which passes through the base 30 of the oven and the bench top 31. A cup shaped member 8 is attached to the magnetron 4 by means of machine screws 9. The cup member has a nitrogen inlet tube 10, the flanged end of which is positioned on a spring loaded connector 14 on the tube 15 inside the compartment 5 which is connected to a supply of nitrogen through a valve 16 on the outside of the oven. With this arrangement, nitrogen under pressure is forced. into the cup member 8 around the exposed parts thereof and between the tuning head 17 (which actuates tuning means inthe resonant cavity) and its close fitting bearing 18 where oxidation or scaling is particularly objectionable as it is in this area that scale tends to jam or freeze the tuning head 17 in the bearing 18. While a substantially gas tight seal is provided between the cup member 8 and the body of the magnetron as well as between a shaft 11 and a bearing 12 therefor in the bottom of the cup member 8 (to be discussed below) there is Sllfilclfil'lt clearance to permit a slight leakage of nitrogen through these seals due to the pressure build-up within the cup. This leakage forces the air out of the cup making the gas therein richer in nitrogen and therefore more inert. The nitrogen passing between the tuning head 17 and its bearing 18 is forced into the chamber 26, the

non-vacuum side of flexible bellows 27 which forms a seal between the vacuum side of the tube and the air or atmosphere side thereof. These bellows 27 stretch or contract as the tuning head is moved axially. By saturating the air in these open or non-vacuum areas of the magnetron with nitrogen, oxidation is greatly reduced although some scaling still takes place. A secondary purpose of this flow of nitrogen to the parts is for cooling, that is to maintain the magnetron tuning head within a certain temperature range to prevent it from being overheated and thereby damaged.

In order to actuate the tuning head 17 during the bakshaft 11 supported in a bearing 12 made preferably of high purity graphite in order to withstand the high temperature (approximately 500 C.) to which the magnetron is heated. The upper end of the shaft 11 carries a flexible coupling 20 to which a tuning nut 19 is welded. The tuning nut 19 fits on the threads of the tuning head 17 which protrude from the magnetron, the flexible coupling permitting engagement of the two threaded members even if the parts are not perfectly aligned. Attached to the lower end of the shaft 11 is a slotted coupling member 21 for receiving a screwdriver shaped driving bit 22 extending up through the bench top 31 and the base 30 of the oven. The bit 22 may be rotated by means of a handle 23 mounted on the bench below and outside of the oven 5 through bevelled gears 24. Turning the handle 23 will result in moving the tuning head 17 axially within its bearing 18, a key 25 cooperating with a slot in the tuning head 17 being provided to prevent any rotation thereof. By rotating the handle occasionally during the baking period, any scale which may have been formed between the tuning head 17 and its bearing 18 will be broken and scraped off before it can freeze the two parts together. Such operation together with the flow of nitrogen enriched air around the parts has resulted in substantially complete elimination of freeze up troubles as experienced heretofore.

By using the flanged nitrogen supply tube 10 in conjunction with the spring loaded connector 14 and the slotted coupling 21, after the resonant cavity of the magnetron has been evacuated and the tube 6 therefor removed or disconnected, the magnetron 4 together with its support 7 and cup-shaped member 8 may be transferred as a unit to a new station for subsequent processing and the remote control tuning actuator and gas supplying means may again be utilized as required (as for the subsequent high potential pulsing operation). In

a 3 I such a case the associated gas supply and shaft driving apparatus is required.

It is to be understood that the above described arrangement is simply illustrative of .the. application of the principles of the invention. Numerous other arrangements may be readily devisedby those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is: t

1.' Apparatus for preventing seizing of a longitudinally slidable tuning member in a close-fitting bearing of a magnetron while the cavities of the magnetron are being exhausted, the end of the tuning member being threaded and extending external of the magnetron, the tuning member and bearing being susceptible to seizing and freezing-up by the formation of oxides thereon when subjected to heat, said apparatustcomprising an oven for heating such a magnetron to a high temperature to facilitate exhausting the cavities thereof, means for exhausting the cavities of the magnetron when in the oven, a support member in the oven for the magnetron, a cup-shaped member having an aperture and a tube connected thereto for admitting inert gas into the cup member, a rotatable shaft extending through the cup member having a resiliently mounted threaded member at one end thereof and a heat resistant bearing therefor in the cup member, means for securing the cup member in substantially gastight relation to the magnetron to surround the external portions of the tuning member and its bearing with the threaded end of the tuning member, clearance being provided between the shaft and bearing in the cup member to permit passing gases from within the cup when inert gasis supplied thereto to envelop the tuning member and bearing therefor in a highly inert and cooling atmosphere to retard oxidation thereof and scale formation thereon, and means disposed external to the oven for rotating the shaft to move the tuning mechanism longitudinally in its bearing to break scale formations therebetween while the magnetron is being heated and exhausted. Y t

2. Apparatus for preventing seizing of a longitudinally slidable tuning member in a close-fitting bearing of a magnetron while the cavities of the magnetron are being exhausted, the end of the tuning member being threaded and extending external of the magnetron, the tuning member and bearing being susceptible to seizing and freezing-up by the formation of oxides thereon when subjected to heat, said apparatus comprising an oven for heating such a magnetron to a high temperature to facili tate exhausting the cavities, a supply tube extending into the oven for supplying inert gas "thereto, a spring loaded connector on the end of the tube, means for exhausting the magnetron while in the oven, a support member in the oven for the magnetron, a cup-shaped member having an aperture therethrough, a tube connected to the aperture for admitting gas to the cup member from the supply tube, the tube on the cup member having an enlarged flanged end for making resilient sealing engagement with the connector, a rotatable shaft extending through the cup member having a resiliently mounted threaded member at one end thereof and a heat resistant bearing therefor in the cup member, means for securing the cup member in substantialytgas -tight relation to a magnetron so that when the magnetron is mounted to the support the enlarged end of the tube engages the connector to supplyinert gas to'tthe tuning member and with the threaded member of the rotatable shaft in operable engagement with the threaded end of the tuning member, clearance being provided between the shaft and bearing in the cup member to permit passing gases from within when inert gas is supplied thereto through the tubes to develop the tuningmember and its bearing in a highly inert and cooling atmosphere to retard oxidation and scale formation thereon, and means disposed external to the oven for rotating the shaft to move the tuning mechanism longitudinally to break scale formations between the tuning member and its bearing while the magnetron is being heated and exhausted.

References Cited in the file of this patent UNITED STATES PATENTS 929,017 W Reynard July 27, 1909 1,461,155 Madden et al. July 10, 1923 2,428,610 Beggs Oct. 7, 1947 2,538,496 Barry Jan. 16, 1951 2,553,749 Clark et a1. May 22, 1951 2,678,761 Warren et a1 May 18, 1954 

